Variable-speed dynamo.



'H. LEITNER. VARIABLE SPEED 'DYNAMO.

APPLICATION TILED 'APR 11. 1912 Patented Apr. 21, 1914 2 SHEETS-SHEET 1.

[IZUCILZW 7M LL15...

ILLEITNER.

VARIABLE SPEED DYNAMO.

Patented A r. 21, 191 1 2 SHEETSSHEET 2.

' HENRY LEITNER, OF LONDON, ENGLAND.

' VARIABLE-SPEED ynamo.

To all 'whom it mag] concern: v

Be it known that I, HENRY LEITNER, a subject of the King of Great Britain, resid- 'ing at Westminster, London, England, have invented new and useful Improvements in Variable-Speed Dynamos, of which the following is a specification.

. This invention relates to variable-speed dynamos of the kind commonly employed in connection' with train lighting and for like purposes, and wherein one or more subsidiary brushes is or are used to control the field-magnet circuitflfor 'self-regulating purposes, .one example ofwhich is shown anddescribed in my former U. S. Patent #863,410 dated August 10, 1907.

The present invention has for its object to provide increased efiiciency in the action of the subsidiary brush or brushes as regards the self-regulating properties of dynamos of this type, whereby theoutput is maintained more ,constantboth as to voltage and current. To this'end according to my invention I reduce'very considerably the extent of the polar arc,and, therefore, the arc of the resulting magnetic flux from the pole to the,armature,'and this I'may accomplish by reducing, and in somecases by dispensing altogether with, t-he usual magnet pole-shoes, and by making the pole-cores or shanks of such a sectional shape-as to constitute eflicient poles; for example, I may make the pole-cores in crossfsection of an elh tical shape, or in the form of atruncated e lipse,

or of a diamond or double-V shape, or of a truncated diamond shape.

To enable the invention to be fully under stood, I will describe it by reference to the accompanying drawings, in which I Figure 1 is a ksemi-diagrammatic view, partly in -se ction,.of a hi-polar dynamo con structed according to the invention, in which two subsidiary brushes are employed in the field circuit. Fig. 2 isa View similar to Fig. 1 illustrating an arrangement in which only one subsidiary brush is employed in the field circuit. I .Fig. 3 is iLVlGW giving in cross section .fouralternat-ive shapes of polepieces, and Figs. sand 5 are viewsshowing some comparative output curves hereinafter explained,

n represents the armature oi the dynamo,

, 5 the commutator thereof, 0, c the fieldmagnets and poles and d the body or yoke. 9, pm the main brushes which supply Specification of Letters Patent.

' Application filed April 11, 1912. Serial No. 690,052.

Patented. Apr. 21, 1914.

made use of, the said brushes being placed midway between the main brushes 6, e to is given in the direction of rotation of the armature indicated by the arrow.

As above described the field magnets and that they constitute eflicient poles. In Fig. 3, I have shown four sections which will give good results in practice, the section it being of elliptical shape, the section 2' in the form of a truncated ellipse, the section 3' of a double-V or diamond shape and the sec-- tion of a truncated diamond shape. It, will be understood, however, that other shapes may be made use of which give rise to the same result.

In machines constructed as above described. a marked advantage is obtained both as regards output and self-regulating properties as compared with the more general design in which it is usual to employ pole-shoes and to make the polar are about 70 per cent. of the pole-pitch or circular distance between the centers of the adjacent poles.

It is well understood that when a dynamo is loaded, the magnetic fiux sufi'ers distortion owing to armature reaction, and the axis of the flux which is normally, that is to say when the machine is not loaded, coincident with the center line of the poles, is displaced in the direction of rotation of the armature. The. effect of limiting the extent of the polar arc, and of the resulting arc oft-he magnetic flux by the construction herein described is, in the first place, to limit or restrict the displacement of the axis of the magnetic flux within a narrower range, and, in the second place, and by reason of this limitation, to give to the subsidizn' t brush or brushes a lead in the direction of rotation.

The amount of subsidiary current or snlr sidiary E. M. F. furnished by the subsidiary brush or brushes when connected between which, together with the said subsidiary. brushes, a certain amount of physical lea-d1 poles 0, c are made of a sectional shape such virtually ii'lcreased the principal brushes of the machine and the shunt field-winding as shown in the accompanying drawings, depends on the angular distance or lead, in the direction of rotation, from the line passing through the center of the pole-pieces, and by giving to the subsidiary brush or brushes a certain amount of physical lead, the effect is obtained that when the machine commences to rotate and excites, the subsidiary bruslror brushes assists or assist in building up the field, but 'this building up, or boosting, effect is reduced to zero when the axis of the magnetic flux becomes coincident with the subsidiary brush or brushes, and may even have a negative value it the axis is displaced still further. \Vith the present construction, therefore, in which the axis of the magnetic flux does not suffer so great a displacement, the E. M. F. of the subsidiary brush or brushes, having a certain amount of lead, although still gradually diminishing proportionately with increase of load and speed, does not so soon, or does not at all, reach this zero value, that is to say, there is a virtually increased lead in the direction of rotation, and a continual though diminishing boosting eilect. In addition to the diminished polar are I may, therefore, give to the subsidiary brush or brushes a greater proportional physical lead relatively to the polar axis than that which is given to the main brushes, that is to say, for example, in a bi-polar machine, the subsidiary brush or brushes may not only be behind or on, but preferably in advance of, a line at right angles to the main brushes. Such an arrangement is illustrated in-F1 g. 2 where the dynamo is shown as being furnished with a single subsidiary brush 9 having the greater proportionate lead above referred to. i As above stated, a dynamo constructed as described is characterized by an increased output, as compared with such machines as hitherto generally constructed. The extent to which the output of the machine is improved. is such that the much less permeable cast-iron may be made use of for the yoke and poles oi the machine. and still a larger output be obtained than from a machine of the usual design and of the same size and having the'more permeable cast-steel yoke and poles. F inrthermore, I also obtain the advantage that the poles can be cast in one piece with the yoke.

Fig. '4 shows the output curves of two similar sized machines designed for train lighting purposes, the curve A representing the output of a machine constructed inaccordance with my former United States patent hcreinbetore referred to, and having cast-steel yoke and poles, while the curve B represents the output of a cast-iron machine of the same size constructed with the thus be obtained'with my improved con struction of dynamo within the limits given by the rising curve C and the drooping curve B by the adjustment or variation of the lead of the subsidiary brush or brushes.

Fig. 5 shows comparative curves of a smaller machine. A bein the curve of an.

original cast-steel machine with normal polar arc, and B that of a cast-iron machine with restricted polar arc, the subsidiary brush being so placed as to give a practically constant output or straight-line curve, after the maximum has been reached. Such a machine as is herein described is specially adapted. in conjunction with accumulators, for the lighting of moving vehicles, such as motor cars, and for railway train lighting, and the like, and for a variety of other purposes in which it is necessary to compensate automatically for varying load and speed, but it is not necessarily confined to these uses. Having now particularly described and ascertained the nature of my said invention, and in what manner the same is to be performed, I declare that while I do not claim in general the construction of a dynamo in which the polar area is entirely or .almost entirely limited to the area of the cross-section of the pole core or shank, what I do claim 1s:-

In a dynamo, the combination with field magnets provided with field windings, an

armature, main line brushes and a subsidiary brush connected with a winding of the field magnets so as to add to the force of the field magnets at low speed, the field magnet poles having their areas adjacent to the armature restricted substantially to the cross-sectional area of the pole-cores to limit the displacement of the axis of the magnetic flux, the main brushes being given. a predetermined lead, and the subsidiary brush being given a sufficiently greater predetermined lead than the main brushes so that at high speed the current through the field coils connected therewith will still add to the strength of the field magnets in a diminished degree and prevent the production of reverse current in said'coils at any time.

HENRY LEITNER.

Witnesses 1 JOHN E. BoUsrrELo, C. G. REDFERN. 

